Question:
Write chemical reactions to show the amphoteric nature of water.
Solution:
The amphoteric nature of water can be described on the basis of the following reactions:
1) Reaction with H2S
The reaction takes place as:
In the forward reaction, $\mathrm{H}_{2} \mathrm{O}_{(i)}$ accepts a proton from $\mathrm{H}_{2} \mathrm{~S}_{(a q)}$. Hence, it acts as a Lewis base.
2) Reaction with NH3
The reaction takes place as:
In the forward reaction, $\mathrm{H}_{2} \mathrm{O}_{(t)}$ denotes its proton to $\mathrm{NH}_{3((q))}$. Hence, it acts as a Lewis acid.
3) Self-ionization of water
In the reaction, two water molecules react as:
